Electrostatic heating apparatus



Oct. 31, '1950 I D. DRUGMAND AZ ELECTROSTATIC HEATING APPARATUS FiledApril 25, 1946 FREQUENCY T CURRENT H 15 -IA, SOURCE.

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Patented Oct. 31, 1950 UNITED l I JELECTROSTATIC HEATING APPARATUSLester D. Drugmand, Milwaukee, Wis., assignor to Cutler-Hammer, Inc.,Milwaukee, Wis., a corporation of Delaware Application April 25, 1946,Serial No. 664,779

4 Claims. (Cl. 219-47) This invention relates to an improvement inelectrostatic heating apparatus, and more particularly to means fordielectric heating of a sheet or web of material or of a coatingdeposited on such sheet or web. The invention is particularlyadvantageous for the drying of ink deposited on a web or sheet of paperpassing through printing machinery.

It has heretofore been a practice in printing to move the printed sheetor web past a blast of hot air or a series of open gas flames for dryingthe ink. These methods are unsatisfactory, as in many installations thepaper passes through the press at a very high speed so that the time ofexposure to the drying medium is very short. Consequently extremely hightemperatures are required which are likely to cause ignition of thepaper should it be slowed down or stopped opposite the heat source.Furthermore, the heat absorption is non-selective, so that both theunprinted paper and the portion covered with ink must be heated.

An object of the present invention is to provide means for drying astream of material in transit by dielectric means.

Another object is to provide means for heating a sheet or web ofmaterial by passing it throug an electrostatic field. 7

Another object is to provide means for drying the ink or color depositedon sheets or webs of paper or the like upon their passage through an.electrostatic field.

Another object is to provide means to facilitate the employment of anelectrostatic field for drying webs or sheets of dielectric material ofrelatively great width.

Another object is to provide means to facilitate the employment of anelectrostatic field for drying moving webs or sheets of dielectricmaterial as they move through or are discharged from a processingmachine.

Other objects and advantages will hereinafter appear.

In accordance with the present invention, the

generation of heat takes place directly in and is confined to the inkdeposit, thus avoiding overheating of the paper, the heat of evaporationof the ink tending tokeep the paper underlying the latter cool.Furthermore, as the dielectric losses in the'paper are low, theimprinted part of the paper surface also remains cool.

Inks such as used for printing newspapers and the like have dielectricloss factors which are several times those of the paper with which theyare used. Hence if such a printed paper is introduced as a dielectricbetween two parallel condenser plates which have impressed therebetweena high frequency voltage, the dielectric losses appear as heat. As theloss factor of those areas which are covered with wet ink is muchgreater than that of the unprinted areas, the losses in and the heatingof the inked part will be much greater, with the. result that the ink israpidly dried or set without overheating of the paper, even should theweb or sheet be slowed down or stopped in its travel between the plates.

The accompanying drawings are illustrative of anembodiment of theinvention.

In the drawing,

Figure 1 is a diagrammatic view of a drying apparatus.

.Fig. 2 is a perspective sketch of a modification of the arrangementillustrated in Fig. 1, while Fig. 3 is a cross section along the line3-3 of Fig. 2.

Referring for further explanation to Fig. l, the same diagrammaticallyillustrates a web H) which is wound from a roll ll onto a roll 12, thelatter being driven by any appropriate means (not shown). Interposedbetween the rolls II and I2, in parallel with the web I!) and spacedtherefrom a short distance on opposite sides thereof are the twoconducting plates 13, I3, each suitably supported by an insulator [4,thus forming a capacitor. Each plate'is connected to one pole of asource [5 of high frequency current. The electric field, between theplates I3, [3, induces dielectric losses in the paper between the platesbut due to the low loss factor of the paper the heat generated thereinis not sufficient to over heat it. However, in the areas where the paperis covered with a layer of moist ink, additional dielectric losses occurin the layer of ink due to the higher loss factor of the latter. Theselosses heat up the ink and dry it rapidly.

Obviously the speed of drying depends upon the resulting dielectriclosses in the ink per unit time.

space between the two plates, .as modified by the web.

Furthermore, if the length of the plates exceeds a certain value for agiven frequency, standing voltage waves will exist on these plates andwill cause an unequal distribution of the energy conversion in thecomposite dielectric between the plates. of the frequency, hence themaximum frequency also limits therate of drying.

The present invention avoids this limitation by passing the energy fromthe source through several smaller series connected capacitors, therebyreducing the relative capacitance of the circuit to permit employment ofa sufiiciently high frequency at a correspondingly higher total voltage.The reduction of the capacitance also overcomes the serious tuningproblem occasioned by The heat energy is, however, a function theemployment of large capacitances at the required high frequency.Furthermore, the dimensions of the individual plates are reduced,thereby not only facilitating the installation and avoiding complicatedstructural features to prevent bending and buckling of the individualplates which would cause variations in the interspace between theplates, but also eliminating the standing voltage wave mentioned above.

Figs. 2 and 3 show an arrangement of plates in accordance with theforegoing for drying of a web of considerable width. Instead ofemploying a single plate on each side of the web, each plate is replacedby a number of coplanar plates. Above the web 28 are shown four coplanarrectangular plates 2!], 2!, 22 and 23. Each plate has a length equal totwice its width, and the width of each plate extends in the direction ofmovement of the web. Asmall air gap is provided between adjacent edgesof the plates so as to electrically insulate them from one another. Theplates are suitably supported and insulated from the machine. Below theweb and opposite to the plates 20 to '23, inclusive, are four plates 24to 27, inclusive. They are of the same proportions as the plates 22 to23, inclusive. The .plates 24 and 25 are arranged with their major axeslongitudinal of the web 28 and therefore at right angles to theupperplates. They are located under the respective outer areas of the upperplates. The plates'2t and 21 are arranged with their major axestransverse to the web 28 and thus parallel to the major axes of theupper plates. They. are interposed between the longitudinal edges of theplates '24 and 25 so that their own longitudinal axes are parallel tothe longitudinal axes of the plates 23 to 23, inclusive. Each plate 26and 27, respectively, is connected to one poleof a source 22 of highfrequency current.

Thus a dielectric current passes from the source 29 successively toplates 26, 2!, 2t, 20, '27 back to the source 29} a second and parallelpath for the dielectric current is from the source 29 to plates 26, 22,'25, 23, 27 back to the source 29.

It will be apparent that this arrangement provides two groups of fourseries-connected dielectric fields, the two groups being connected inparallel. Thus the effective capacitance of each group for the samevertical spacing of the plates is substantially one quarter of thecapacitance of a single capacitor of the same total plate area, whilewith the same voltage gradient in the interspace the arrangement ofFigs. 2 and 3 enables the employment of four'times the voltage for thesametotal energy dissipation over a given area as that of thearrangement illustrated in Fig. 1.'

By connecting two sets of series-connected capacitors in parallel asshown in Fig. 2 the mar representing one of the parallel branches may beomitted, the remaining areas cooperating with one-half of the width ofthe web 28. It is also obvious that the, arrangement of Fig. 2 may befurther modified by increasing or decreasing the number of capacitorsections which are connected in series across the source of energy.

While the invention hasbeen described as applied to the drying of aprinted paper web, it may also be applied generally to the drying of asuccession of individual printed sheets as they leave a press or otherprocessing machine. Furthermore, the invention is applicable to the.heating for drying or curing of any dielectric material in web, ribbon,or sheet form which may be passed in a substantially continuous orintermittent stream through the apparatus described.

The apparatus is capable of various modifications which will be apparentto those skilled in the art as coming within the scope ofthis in-.vention.

T I cIaim:

Apparatus for dielectric heating of sheet materiaL'comprising, a sourceof high frequency energy, a first group and a cooperating second group,exceeding two in number, of coplanar conducting plates, the plates ofthe respective groups being spaced in parallel relation to each other toprovide a corresponding number of dielectric fields, the interspacebetween each pair of corresponding plates aifording a passage for amaterial to be heated while moving through said dielectric fields, andcircuit connections for connecting said dielectric fields'in series withone another across said source.

'2. Apparatus for dielectric heating of sheet material while in transitbetween given points over a given path, comprising, a source of highfrequency energy, a first group and a cooperating second group,exceeding two in number, of coplanar conducting plates, the plates ofthe respective'groups being spaced in parallel relation to said path onopposite sides thereof, said plates providing a plurality, exceeding twoin number, of "dielectric fields affording a passage for the material tobe heated across said dielectric fields, and circuit connections forconnecting said dielectricfields 'in series with one another across saidsource. I

3. Apparatus for dielectric heating of sheet material while in transitbetween given points over a given path, comprising, a single source ofhigh frequency current, two groups of conducting plates, each groupexceeding two in number, the plates of one group being so arranged inspaced parallel relationship to the plates. of the other group as toprovide a number of dielectric fields exactly corresponding to the totalnumber of plates in both groups, the space between said groups of platesaffording a passage for sheet material to be heated while moving throughsaid dielectric fields, circuit connections arranged to dividesaiddielectric fields into two groups, the dielectric fields of eachgroup being connected in series across said source, and the two groupsof-fields' being connected in; parallel with each other.

4. Apparatus-for dielectric heating of sheet material while intransit'between given points over a, given path,- ycomprising, a singlesource of high frequencycurrent, at least eight like conducting platesof rectangular contour, each plate havinga length -e'qual to twice itswidth, one

group of four of said plates being symmetrically arranged in the formofa rectangle with one both groups being such as to provide eight dielec-A trio fields, each four of said dielectric fields being connected inseries with each other, and the two groups of four series connecteddielectric fields being connected in parallel with each other.

LESTER D. DRUGMAND.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,231,457 Stephen Feb. 11, 19412,288,269 Crandell June 30, 1942 2,333,412 Crandell Nov. 2, 19432,342,846 Crandell Feb. 29, 1944 2,397,615 IVIittelmann Apr. 2, 19462,436,732 Rowe Feb. 24, 1948 FOREIGN PATENTS Number Country 7 Date518,691 Great Britain Mar. 5, 1940

